It seems scarcely credible that when the three surviving members of Led Zeppelin reunited for their one-off show in London in 2007, 20 million people applied for tickets. Though they bestrode the world like a priapic, all-devouring monster of depravity in the 1970s, the years following their split in 1980 – caused by the death of drummer John Bonham – were not kind to them. Critical orthodoxy held them to be dinosaurs, representatives of all that was worst about rock excess in both behaviour and music.